Universität Stuttgart
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Item Open Access Comparison and analysis of web vulnerability scanners(2019) Lis, AlexanderWithin the last years the commercial relevance of web applications increased steadily. They developed from simple information sharing platforms to serious business applications like online-banking, e-commerce and social media platforms. Unlike most other technologies, web-based applications are accessible from around the world continuously. Additionally, they are very susceptible for vulnerabilities as there are various technologies interacting. These factors render web applications to very attractive targets for criminals because they are often easy to attack, globally accessible and yield valuable exploits. As a consequence, much effort was put into research to prevent, detect and eliminate web application vulnerabilities. However manual security audits are time-consuming, costly and demand expertknowledge. Web vulnerability scanners tackle this problem. They are programs that test web applications for the existence of vulnerabilities. Additionally they categorize and report them. Because these tools work automatically, faster as humans and reduce the necessary knowledge in network security, they became an interesting supplementation to traditional security audits. On the other side web vulnerability scanners also have their limits. They can not test for the absence of vulnerabilities and thus produce false positives or miss weaknesses. Furthermore previous research has shown that there are also vulnerability classes that are especially intricate to detect like stored SQL injections or stored cross-site scripting vulnerabilities. Nonetheless web vulnerability scanners show very much potential and there is a growing interest into automatic web application testing. This is reflected in the increasing diversity of commercial web vulnerability scanners that can be found online. Thus this thesis compares and examines three web vulnerability scanners, namely Acunetix, Arachni and w3af. Focus is set on delineating the current capabilities and limits of state-of-the-art vulnerability scanners.Item Open Access Verifiable tally-hiding E-voting with fully homomorphic encryption(2020) Hasler, SebastianAn E-voting system is end-to-end verifiable if arbitrary external parties can check whether the result of the election is correct or not. It is tally-hiding if it does not disclose the full election result but rather only the relevant information, such as e.g. the winner of the election. In this thesis we pursue the goal of constructing an end-to-end verifiable tally-hiding E-voting system using fully homomorphic encryption. First we construct an alteration of the GSW levelled fully homomorphic encryption scheme based on the learning with errors over rings assumption. We utilize a key homomorphic property of this scheme in order to augment the scheme by a distributed key generation and distributed decryption. This leads to a passively secure 4-round multi-party computation protocol in the common random string model that can evaluate arithmetic circuits of arbitrary size. The complexity of this protocol is quasi-linear in the number of parties, polynomial in the security parameter and polynomial in the size of the circuit. By using Fiat-Shamir-transformed discrete-log-based zero-knowledge proofs we achieve security against active adversaries in the random oracle model while preserving the number of 4 rounds. Based on this actively secure protocol we construct an end-to-end verifiable tally-hiding E-voting system that has quasi-linear time complexity in the number of voters.Item Open Access Informelle Sicherheitsanalyse der Sequent Tech Identitäts- und Zugriffsmanagementkomponente(2022) Vatic, AmelDie IAM-Komponente wurde von Sequent Tech Inc. für ihre E-Voting-Anwendung entwickelt und anschließend als eigenständige Software-Komponente veröffentlicht. Sie bietet Funktionalität zur Authentifizierung und Autorisierung von Benutzern in einem Anwendungssystem. In dieser Arbeit wird eine informelle Sicherheitsanalyse der IAM-Komponente und der in der Komponente definierten Authentifizierungsprotokolle angefertigt. Die Authentifizierungsprotokolle legen dabei jeweils fest, wie sich die Benutzer bei der IAM-Komponente authentisieren müssen. Die Grundlage dieser Analyse bildet dabei eine ausführliche Beschreibung dieser Komponente und ihrer Authentifizierungsprotokolle, die im Rahmen dieser Arbeit ebenfalls angefertigt wird. Von besonderer Interesse ist dabei das Single-Sign-On Authentifizierungsprotokoll SmartLink. Nachdem wir die Beschreibung angefertigt haben, werden die IAM-Komponente und ihre Authentifizierungsprotokolle informell analysiert. Dabei beginnen wir mit der Identifikation der Annahmen und der Angreifermodelle, die für die Sicherheitsanalyse zu Grunde gelegt werden. Die drei Sicherheitsziele, die in von der IAM-Komponente erfüllt werden müssen sind dabei Authentifizierung, Autorisierung und Session Integrity. In der darauffolgenden Sicherheitsanalyse werden die Komponente und die Authentifizierungsprotokolle bezüglich allen Sicherheitsdefinitionen überprüft.Item Open Access Joint state composition theorems for public-key encryption and digital signature functionalities with local computation(2020) Küsters, Ralf; Tuengerthal, Max; Rausch, DanielIn frameworks for universal composability, complex protocols can be built from sub-protocols in a modular way using composition theorems. However, as first pointed out and studied by Canetti and Rabin, this modular approach often leads to impractical implementations. For example, when using a functionality for digital signatures within a more complex protocol, parties have to generate new verification and signing keys for every session of the protocol. This motivates to generalize composition theorems to so-called joint state (composition) theorems, where different copies of a functionality may share some state, e.g., the same verification and signing keys. In this paper, we present a joint state theorem which is more general than the original theorem of Canetti and Rabin, for which several problems and limitations are pointed out. We apply our theorem to obtain joint state realizations for three functionalities: public-key encryption, replayable public-key encryption, and digital signatures. Unlike most other formulations, our functionalities model that ciphertexts and signatures are computed locally, rather than being provided by the adversary. To obtain the joint state realizations, the functionalities have to be designed carefully. Other formulations proposed in the literature are shown to be unsuitable. Our work is based on the IITM model. Our definitions and results demonstrate the expressivity and simplicity of this model. For example, unlike Canetti’s UC model, in the IITM model no explicit joint state operator needs to be defined and the joint state theorem follows immediately from the composition theorem in the IITM model.Item Open Access Beschreibung und Analyse der W3C Browser Push APIs(2024) Lüers, AlinaDie W3C Push API bietet die Möglichkeit der asynchronen Kommunikation zwischen einem Browser und einem Anwendungsserver. Der Anwendungsserver kann Push Nachrichten an einen Push Service senden. Der Push Service speichert die Nachricht bis der Browser erreichbar ist oder die Nachricht verfällt. Wenn der Browser die Push Nachricht erhält, wird die Push Nachricht an den Service Worker weitergeleitet, der die Nachricht verarbeitet und gegebenenfalls dem Nutzer anzeigt. In dieser Arbeit wird die W3C Push API zunächst abstrakt beschrieben und darauf aufbauend eine informelle Sicherheitsanalyse durchgeführt. Dafür werden zunächst die der Analyse zu Grunde liegenden Angreifermodelle und Annahmen definiert. Anschließend werden die Sicherheitsziele Vertraulichkeit, Privacy, Verfügbarkeit, Authentifizierung, Autorisierung und Session Integrität untersucht. In der Analyse konnten dabei keine neuen, gravierenden Sicherheitsprobleme festgestellt werden. Anschließend wird die Implementierung der Push API in Firefox näher betrachtet. Dabei wird der Push Service autopush beschrieben und es werden die zusätzlichen Sicherheitsmaßnahmen aufgezählt.Item Open Access XSS in issue tracking systems(2021) Hildebrand, MoritzToday, virtually every software project, especially in a collaborative and distributed setting, is managed through an issue tracking system (ITS). As developers rely heavily on ITSs, the risk of cyberattacks and their associated impact increases. An interesting particularity of ITSs is that, compared to conventional web applications, the attack surface is extended through additional input interfaces such as email or version control systems (VCSs).This bachelor thesis develops a methodology to test ITSs for Cross-site scripting (XSS) vulnerabilities via these ITS-specific input interfaces. Exemplarily, we implement the developed methodology for the input interfaces email and Git and test it on the three open-source ITSs Redmine, MantisBT, and Trac.Item Open Access Overview on web authentication and authorization protocol security evaluations(2025) Schäberle, VictoriaWeb authentication and authorization protocols such as OAuth 2.0 and OpenID Connect are widely used and have become established standards in the single sign-on (SSO) ecosystem. They enable users to grant third-party applications access to their resources and to use diverse online services conveniently and securely, while reducing the risks associated with password-based authentication. However, incorrect implementations have repeatedly led to severe vulnerabilities, ranging from token theft to account compromise. These risks highlight the importance of understanding the security properties and weaknesses of these protocols. This thesis investigates the security of OAuth 2.0 and OpenID Connect by providing a structured overview of existing evaluations, considering both foundational and widely cited studies as well as more recent contributions. Both scientific and non-scientific sources are considered, including formal analyses, empirical studies, and protocol specifications. Typical attacks and vulnerabilities are summarized and categorized into four fields, which include formal, empirical, protection-centered, and investigations of specific attacks and mitigations. The review highlights approaches that develop tools for empirical evaluation, focus on mobile applications, or analyze relying parties (RPs) and identity providers (IdPs). The methodology of the empirical studies examined range from active and passive attack strategies to white-box and black-box analyses. By synthesizing these findings, this thesis reveals a persistent gap between the formal security of the protocols and recurring weaknesses in real-world implementations. This gap underscores the need for continued research, clearer developer guidance, and systematic auditing.Item Open Access Mechanized modeling and security proofs for web protocols(2025) Würtele, Tim; Küsters, Ralf (Prof. Dr.)The Web plays a central role in modern life - not only for news and social interactions, but also in security-critical applications such as banking and healthcare. Many of these applications rely on standardized protocols, for example, for authentication and authorization. Hence, the security of many applications on the Web depends on the security of these protocols. Studying the security of protocols - not just on the Web - has been an active area of research for over four decades. An important branch of this research focuses on applying formal methods to obtain rigorous, formally proven security guarantees. However, in the context of Web protocols, the complexity of the underlying infrastructure - with multiple layers of sub-protocols and intricate interactions between involved parties (e.g., in-browser communication between websites) - poses significant challenges for such analyses. Yet this complexity must be captured, since even subtle design details may have security implications, as demonstrated by past attacks. This thesis advances the state of the art in Web protocol security analysis in several ways. First, we present a formal security analysis of the FAPI 2.0 protocol family, developed and used in high-risk domains such as banking and healthcare. Our analysis accompanied the development of the FAPI 2.0 protocols and is based on the most comprehensive and detailed security analysis framework for Web protocols to date, the Web Infrastructure Model (WIM) - a pen-and-paper Dolev-Yao-style model that captures many aspects of the Web environment, and in particular, many details of the inner workings of Web browsers. To faithfully model FAPI 2.0, we extend the WIM in several ways, for example, by introducing communication channels for push messaging and support for so-called HTTP Message Signatures. These extensions are derived from relatively recent, yet already established Web standards, and are therefore of independent interest for keeping the WIM up to date. Our analysis - the largest based on the WIM so far - uncovered multiple new attacks that led to fixes in the now-finalized FAPI 2.0 standards, and started an ongoing effort within the standardization body responsible for FAPI 2.0 to apply formal analysis to more and more of their standards. At the same time, this work illustrates the limitations of pen-and-paper proofs: our analysis spans more than 100 pages of hand-written, manually verified proofs. Hence, mechanized verification promises more reliable results, but existing mechanized tools struggle with the level of detail and resulting model size required for realistic Web models. To bridge this gap, we contribute to the development of DY*, a mechanized Dolev-Yao-style protocol analysis framework that supports implementation-level executable models, highly modular proofs over an explicit global trace, an extensible equational theory, and can cope well with unbounded data structures, loops, and recursion. While the long-term goal is to develop DY* into a Web protocol analysis framework - akin to the WIM, but fully mechanized - it has already been used in several nontrivial case studies, including the first formal analysis of the Signal protocol with an unbounded number of ratcheting rounds. Finally, as a first step toward such a mechanized Web protocol analysis framework based on DY*, we use DY* to analyze the immensely popular ACME certificate issuance protocol. In the course of this analysis, we extend DY* with authenticated channels, an enhanced equational theory to more precisely capture the properties of digital signatures, and develop a methodology to execute DY* models against real-world implementations. Our analysis is the first of the final ACME standard and ranks among the most detailed mechanized protocol security analyses to date - our executable model can even interact with real-world servers.Item Open Access Übersicht über das Hacker-Ökosystem(2018) Geyer, SimonIn einer zunehmend vernetzten Welt nimmt Informationstechnologie eine zentrale Rolle in der Gesellschaft ein. Daher haben Hacker, als Angreifer auf IT-Systeme, einen starken und teils gefährlichen Einfluss auf die Gesellschaft. Diese Arbeit verfolgt das Ziel, anhand von Technologien und existierender Literatur einen Überblick über das Hacker-Ökosystem zu erstellen. Dabei wird zunächst auf Angreifer selbst und eine mögliche Klassifikation eingegangen. Daraufhin werden relevante Aktivitäten von Angreifern thematisiert. Davon ausgehend werden wirtschaftliche Aspekte wie der Handel auf Untergrundmärkten zwischen Hackern erläutert. Dazu wird auf Kryptowährungen wie Bitcoin und deren technische Funktionsweise eingegangen. Ferner werden die Auswirkungen von Angriffen auf IT-Systeme diskutiert. Zum Abschluss wird auf Darknets sowie Anonymisierungstechnologien eingegangen. In diesem Kontext wird die Funktionsweise der beiden Technologien Tor und I2P näher erläutert.Item Open Access Applications for arithmetic tuples(2022) Schieber, MikaSecure Multi-Party Computation (SMPC) is a subfield of cryptography that allows multiple parties to compute a function without disclosing the inputs. Different types of specialised computation of specific (sub)functions are used to make SMPC computations more efficient. A recently published paper introduced Arithmetic Tuples, a new approach for evaluating multivariate polynomials and thereby, arithmetic circuits, in a minimal number of rounds and with practicable precomputation. In this thesis, we demonstrate the practicality of the new approach by applying it to a variety of real-world applications in which it has the potential to be particularly effective. These applications are multiplexers, permutations, demultiplexers and prefix products, which include functions with several outputs. We analyze each application and compare Arithmetic Tuples to the existing approaches Beaver Triples and Binomial Tuples. Comparison criteria are the number of rounds, the number of elements to be precalculated and the number of elements to be communicated.